The belt-driven tape cartridges of the Von Behren patent, U.S. Pat. No. 3,692,255, incorporated herein by reference, are commonly referred to as "data cartridges." A data cartridge typically includes a housing defining a thin, generally rectangular enclosure. The housing contains a length of magnetic recording tape which is wound upon a pair of tape reels. The magnetic recording tape is driven by an elastomeric drive belt which, in turn, is driven by a single, reversible drive motor. The drive belt provides rapid acceleration and deceleration of the recording tape in either direction. The drive belt is stretched along a drive belt path generally defined by a drive roller, a pair of corner rollers, and part of the tape pack wound on each reel.
Data cartridges must meet minimum tape tension specifications while simultaneously operating within maximum allowable drive force specifications. The tape tension must not fall below a certain level as the tape passes from spool to spool or else contact between a read/write head and the tape will be insufficient to allow successful data transfer. Conversely, the force required to rotate the cartridge drive roller cannot exceed the power rating of the motor in the associated drive. As both tape tension and drive force are dependent on friction within the cartridge, all friction sources must be controlled.
For example, a drive roller rotatably mounted on a drive roller shaft is one source of friction that must be controlled in a data cartridge. The friction between a drive roller and its shaft is referred to herein as the "drive roller drag force" or "drag force." To achieve the desired tape tension characteristics, it is desirable for the drive roller drag force to be as low as possible and as stable as possible over the life of the data cartridge. According to one approach, the desired low levels of drag force have been sought by applying a lubricant between a drive roller and its shaft. One kind of lubricant that has been used includes solid fluorinated resin, e.g., polytetrafluoroethylene (PTFE), particles dispersed in a nonfluorinated, e.g., hydrocarbon-based, grease.